George Dvorsky

NASA scientists working on the Kepler Mission have discovered an unprecedented solar system, in which two planets with vastly different densities and compositions are locked in a surprisingly close orbit around their star. The finding shows that there is much greater diversity in the composition of solar systems than we'd previously thought.

Prior to our discovery of exoplanets, our solar system offered a standard blueprint for astronomers speculating about what other solar systems might look like — namely, rocky planets on the inside, and large gas giants farther out. Then, with the discovery of enormous inner-system gas giants, our conceptions of what other systems might look like took a drastic turn. And now, with the discovery of these two new exoplanets, our imaginations are proving to be completely inadequate.

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This newly discovered system is called Kepler-36, and it's about 1,200 light years away. One of its planets is a rocky super-Earth about 1.5 times the size of our planet and 4.5 times the mass. Its companion, a Neptune-like gaseous planet, is 3.7 times the size of Earth and eight times the mass. And they're very close to each other – about 30 times closer than any pair of planets in our solar system.

Because their orbital distance varies by only 10%, the view of the Neptune-like planet from the rocky planet must at times be pretty spectacular.

The new solar system, which the Kepler scientists describe as "extreme," will likely have an impact on emerging theories about planet migration and orbital rearrangement. Prior to this discovery, scientists had assumed that small, rocky planets form in the hot part of the inner solar system, and that bigger, less dense planets can only form far away from the host star, where it's cool enough for volatile material like water ice and methane ice to collect. And it's thought that, in some cases, gas giants can slowly creep their way into the inner solar system, annihilating or ejecting the low-mass inner planets.

But the discovery of Kepler-36 messes this all up, sending the scientists straight back to the drawing board. Specifically, astronomers will have to figure out how the two planets with such different densities in nearly identical orbits both got there and survived — a configuration the Kepler team described as "puzzling."